The present invention relates generally to an improved construction coupling member in cameras or other types of devices, and it relates more particularly to the assembly of a pair of parts which interfit in a rigid or slidable manner.
A conventional procedure for eliminating looseness between a pair of interfitting members is know as an interference fit. However, in accordance with the interference fit, an excess of material on the peripheral surface of a first member must be ground or pressed and thereby broken by the wall of another or second member in which the aforesaid first member is fitted, thereby necessitating an expenditure of much time and effort in assembly, and hence lowering in operation efficiency. In addition, in case the aforesaid interference is unreasonably large, then there results strains in the both members, when one member is fitted into another. Still further, the interference fit finds its application only in providing rigid fits, and thus fails to provide a sliding fit between the both members.
For this reason, for high-precision parts for use in a camera, which should avoid strains of the above type, the aforesaid interference fit is unsuitable, but a clearance fit is applicable in which one member is fitted into another with a minimum of clearance. In the meantime, it is well known that a transitional fit which is expected to provide precise fit between a male member and a female member when both members are assembled with each other. However, this transitional fit is not a suitable solution to the aforesaid problem because not only a clearance but also an interference may occur between both members as the case may be. The reason why the aforesaid clearance fit is unsuitable is that even if the diameter of a hole in one member and the outer diameter of another member fitted therein are manufactured to the same diameter, there necessarily occurs dimensional errors in the finished parts thus providing a possibility of causing an interference fit. In such a case, however, a tolerance is provided for the dimensions of the respective members in the design stage so as to provide a desired clearance between the two members. However, the provision of such a tolerance leads to an eccentricity between the assembled parts, if the resulting clearance is too large, and such an eccentricity cannot be neglected. In other words, the aforesaid eccentricity exerts an adverse effect on the performance and quality of the devices beyond their allowable limits. This is particularly true in the case of a lens barrel for use in an optical system of a camera, because such clearance fit having unexpected large clearance would result in misalignment of the optical axes of the respective lenses. For this reason, a clearance between the two interfit parts should be minimized, and then the tolerances for the parts should be strictly controlled although there arises an increase in manufacturing costs of parts. Even if an error or deviation in clearance beyond the specified limits is of no consequence for a particular interfit pair of parts, an accumulation of errors of this kind, such as in the case of a lens barrel which includes a plurality of such fits, would lead to an extreme lowering in the performance of the optical system of a camera.
FIG. 1 of the drawing herein shows a plurality of fits incorporated in a lens barrel of a camera. The fits shown at 1 and 15 are classified as follows:
______________________________________ Rigid Fit Normal Slidable Fit Smoothly Slidable Fit ______________________________________ 1 2 3 4 13 7 5 6 8 9 10 11 12 14 15 ______________________________________
As can be seen from the above, the lens barrel and the like in a camera includes a plurality of fits of the subject type. Accordingly, even if the looseness in one fit may be negligible, accumulation of such looseness in a plurality of fits can be by no means neglected. For this reason, dimensional accuracy of the respective parts should be strictly controlled. This is a particularly critical problem in the case of a lens barrel having a further complicated construction or devices including a plurality of fits of this type.
Definitions of the terms appearing in the above Table are as follows: By a rigid fit is meant a fit in which one member is rigidly fitted another by using small-sized screws and the like; by a normal slidable fit is meant a fit in which one member fitted in another may be relatively slidable, when an external force strong enought to move one member is applied thereto; and by a smoothly slidable fit is meant a fit between high-speed operating portions associated with an automatic diaphragm operation.